The invention relates to a method for operating a comminuting device, in which method a comminuting rotor is driven by a driving unit at least comprising a rotary current electric motor, via a non-positive traction drive, in particular a belt drive, wherein said rotary current electric motor is energized by a controlled frequency converter, for operating the comminuting rotor at a predetermined rotational speed during the normal operating phase, and wherein a degree of slip of the traction drive is determined and monitored and the rotary current electric motor is controlled for being powered off if a first slip threshold value is exceeded. The invention also relates to a comminuting device for carrying out such a method.
Such comminuting devices or such a method for operating the same are well known in this field and can be used for a variety of materials to be comminuted, such as wood, domestic waste, industrial waste, production remainders etc. To provide the comminution forces that are required, the output power of the electric motor of such a comminuting device may be several 10 KW up to several thousand kW. Here the material to be comminuted is frequently fed to the comminuting rotor while tools mounted to the comminuting rotor act upon the material to be comminuted. Depending on the construction type, the comminuting rotor rotates at a speed of several revolutions up to several hundred revolutions per minute. Considering that with many kinds of materials to be comminuted the comminution process is not performed in a smooth manner, but may be shock-loaded, the requirements are high concerning the stability of the device and particularly the mounting of the rotating parts.
The use of a non-positive traction drive often turns out to be an advantageous alternative to the gear drive mechanism which, too is frequently used and in which an electric motor is connected to the comminuting rotor via a gear mechanism. Depending on the specific application, mechanical gear mechanisms may produce strong running noises or may lead to a harsh, impact-loaded operation of the comminuting device, accompanied by all relevant drawbacks such as noise, vibrancy, and high loads of individual machine elements. Particularly in the case of jamming caused by the occurrence of uncomminutable extraneous materials, the gear mechanism may be severely damaged and shafts may even break. The use of a non-positive traction drive, particularly a belt drive, disposed between the rotary current motor and the comminution rotor turned out to be advantageous, above all with such comminution process. Such a traction drive is relatively resistant to impact loads and has a damping effect on the entire electro-mechanical drive system. If used in such comminuting devices, said belt drive which otherwise has a number of drawbacks such as its design size and wear characteristics, has the advantage that it slips when extraneous material occurs among the material to be comminuted and thus prevents damage to the drive system. For example, if it is detected in such comminuting devices that slip occurs which exceeds a predetermined slip threshold value, the electric motor may be controlled for being powered off.
A comminuting device of this type as well as a method for operating the same are disclosed for example in the German Offenlegungsschrift DE 10 2008 061 734 A1.
Conventional belt drives for comminuting devices are however subject to considerable wear, which results in comparatively short maintenance intervals that must be observed. Further, the operation of such comminuting devices can be complicated because depending on the material to be comminuted it may require frequent stoppage or reversing of the rotor if comminuting material has accumulated. The interruption of the comminuting process can often not be prevented, even if the feeding rate of the material to be comminuted is reduced. It is therefore an object of the present invention to improve a conventional method for operating comminuting devices of this kind or such a comminuting device in such a manner that the above-described problems are removed at least partially.